Cultivate in coco coir
Can you grow in coco coir? Yes, you can even get a nice result.
For decades, nurseries have used rock wool for their plants. A plant does actually not need soil at all. The soil is there to hold the plant steady and to store water and nutrients, but both of those qualities stone wool have too.
Now, however, the nurseries have switched to a completely different product. The product is coco coir. Coco coir has been known as a growing material for some years and has gone in and out of the market. The reason is that it may contain bacteria that are not beneficial to plants. It has often been a matter of unripened coco coir that has been used, but now that part has been checked, and if you choose a good product, the benefits of coco coir are great.
Holds water but cannot get waterlogged
The advantage of coco coir is the many fibres that both provide the amount of oxygen that good soil should have, and drain and absorb water at the same time, so it is able to hold water for a longer time.
Coco coir is not the same as growing in sphagnum. You have to feel it / press it to feel the moisture level. After 14 days/3 weeks, the plants need a bit more fertilizer than for example plants grown in sphagnum and if you have organic fertilizer such as cow or horse manure, then mix it with the coco coir.
The potato grow bag gives the potatoes an optimal start.
Coco coir potatoes
A potato grow bag is a waterproof plastic bag with fine coco coir. The coco fibres are compressed in a block you can take out and put in a bucket with four litres of water. After a good half hour, the block swells up and should be put back in the bag. It is ideal for potatoes, but can also be used for tomatoes or cucumbers, for example.
At first glance, I thought there was very little soil in the bag to give a nice yield, but we will have to see. I need to try the method. Otherwise, the alternative is to use a bag with a block to give the potatoes a really good start in a bright window ledge and then transplant the block without the bag in the ground outside, where it can continue to grow. By the way, remember to make three holes in the bottom of the bag for drainage.
Make your own plant bag
Buy a block of coco coir. It weighs 10 pounds. Place it in a wheelbarrow and pour in twenty litres of water, then you will have 70 litres of coco coir. I would either put it clean in a sack or mix it with organic fertilizer, for example, 1/3 horse manure and 2/3 coco coir, and then it's just a matter of cutting the holes for the tomatoes.
Remember a black sack absorbs heat, but the ground does not get hot. Clear plastic absorbs heat to the ground. In a greenhouse, clear plastic can heat the ground so that it gets too hot, but you can get a green bag, or white, for the greenhouse. Otherwise, black in the greenhouse is better than clear.
Om Lars Lund
Danish horticulturist and journalist
Lars Lund has for many years engaged in the garden and greenhouse. Lars has published many books about greenhouses, and he has participated in many Danish horticultural TV shows. He is a walking garden encyclopaedia, and he has answers for most basic cultivation questions – also the more ambitious ones.